[slabity]

> In order to replicate the functionality of an access point, the device needs to support all 3 bands (2.4/5/6), not just have a slot for whichever single band I want to support.

Many cards support multiple bands concurrently. Some of these devices have multiple slots as well, and if it doesn't you can get an NVMe to mPCIe adapter to enable a second slot. I personally use a Mediatek card for dual-band 2.4GHz + 6GHz and a USB adapter for the 5GHz band (mostly because I don't have an adapter for fitting more than 4 antennae).

> That DIY setup has a lot more compute for routing, but actually does worse in trying to be used as an actual (wireless) access point (and still costs more).

You don't need a lot of compute for routing packets, especially if you are able to set up flowtables and bypass most of that processing anyways. The extra compute is excellent for other services that you might set up on it though, which is why I explicitly mentioned it's a good starting point for a home lab.

All that aside, the real cost of DIY isn't the dollar amount. It's the time and effort required to set it up and maintain it. The only point I mentioned about cost is that it's significantly cheaper than it was a few years ago. If all you want is to reduce cost then it's unlikely you can beat recycling an old desktop computer with an additional 6E card thrown in.